Active measurements or active probing has long been an accepted method for determining performance parameters of communication networks, e.g. packet-switched networks. The basic concept is to transmit probe packets from a sender towards a receiver. Each probe packet is time stamped on both sides.
The measurement endpoint (MEP) and measurement intermediate point (MIP) functionality and capabilities depends on the network technology deployed. For an Internet Protocol (IP) network the MEP functionality is typically based on Internet Engineering Task Force (IETF) Two-Way Active Measurement Protocol (TWAMP), IETF Internet Control Message Protocol (ICMP) or the proprietary Cisco Service Level Agreement (SLA) protocol. For Ethernet and MultiProtocol Label Switching (MPLS) networks the MEP and MIP functionality can be based on ITU-T Y1731. For MPLS-Transport Profile (MPLS-TP), MIP and MEP functionality may also be based on IETF RFC 6371.
The above technologies are capable of measuring performance metrics such as one-way delay, round-trip time, loss, jitter and throughput. Further, extensions to TWAMP enable estimation of available path capacity.
In IP networks many operators often rely on Iperf. This is a tool for measuring mainly Transmission Control Protocol (TCP) throughput. It also reports on jitter, round-trip times and loss. The tool is to some extent a de-facto standard among network operators.
The IETF IP Performance Metrics (IPPM) working group has defined two IP active measurement protocols: One-Way Active Measurement Protocol (OWAMP) and Two-Way Active Measurement Protocol (TWAMP). OWAMP is designed for measuring one-way packet delay and one-way packet loss between two hosts. TWAMP is based on OWAMP. TWAMP is designed for measuring one-way and two-way (round-trip) packet delay and packet loss between two hosts.
The standard TWAMP consists of two protocols: the TWAMP control protocol and the TWAMP test protocol. The TWAMP control protocol is used to initiate, start and stop TWAMP test sessions. The TWAMP test protocol is used to exchange TWAMP test packets between two TWAMP hosts or endpoints. Test sessions can also be configured without the TWAMP control protocol and this is known as TWAMP light.
The standard TWAMP measurement architecture is usually comprised of only two types of hosts with specific roles. This is known as the two-host implementation. One host plays the role as the control-client and session-sender and the other host plays the role as the server and the session-reflector. The host that initiates the TWAMP control TCP connection takes the roles of the control-client and session-sender. The host that acknowledges the TWAMP control TCP connection accepts the roles of the server and session-reflector. In real-life network deployment, each host may participate in several active sessions at the same time, both as control-client/session-sender and server/session-reflector.
In a TWAMP test session, packets are time stamped, tagged with sequence numbers and transmitted from a session-sender to a session-reflector. The session-reflector time stamps the incoming packets, creates new test packets (one packet is created for each test packet received by the session-reflector) and sends them to the session-sender as soon as possible. Using these time stamps and sequence numbers, the session-sender can then calculate the one-way delay, jitter and packet loss for the session in both the forward path and the reverse path.
FIG. 1 illustrates the Evolved Packet System (EPS) network elements along with the interface names. The EPS consists of two main parts; the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) which is the wireless access network, i.e. the set of all E-UTRAN Node B (eNB) elements, and the Evolved Packet Core (EPC) network which corresponds to the rest of the network elements. The EPS elements thus provides access control and security, routing and forwarding, mobility management, radio resource management and network management.
Below is a short overview of what each element is responsible for:
eNB provides Long-Term Evolution (LTE) radio access via the LTE-Uu interface to the user equipment (UE). As part of this activity it manages the radio resources such as the radio bearer.
E-UTRAN Node B (eNB) is connected to the Serving GateWay (S-GW) via the S1-U interface. S-GW routes and forwards user data packets. The S-GW is further connected to the Packet data network GateWay (P-GW) via the S5/S8 interface. P-GW is the router that connects the EPC to other packet-based networks such as the Internet, illustrated as IP services in FIG. 1, over the SGi interface
The Mobility Management Entity (MME) is the control node for the radio access network. It keeps track of idle UEs, it is involved in bearer activation and deactivation and is also responsible for selecting which S-GW to use. The MME is connected to the eNBs via the S1-MME interface and to the S-GW via the S11 interface.
The Home Subscriber Server (HSS) is a centralized entity holding user-related information. The HSS is connected to the MME via the S6a interface.
To manage the sparse radio resources in an efficient way the radio bearers connecting the UE to the eNB can be released during periods of inactivity. This also reduces the power consumption in the UE. When the radio bearers are inactivated, the UE is put in idle state. The MME keeps track of the UE and inactivated radio bearers during the idle state.
When data is available for the idle UE, the MME finds the UE by paging the eNBs. The UE is moved to the connected state, the UE-related information is re-created in the E-UTRAN and the radio bearers are re-established. This is called the idle-to-active transition. A similar process takes place for the case when the idle UE has data to send to the network.
Each radio bearer is associated with a Quality of Service (QoS) Class Identifier (QCI) spanning from 1 (high priority) to 9 (low priority) that is determined for the type of communication between the UE and another endpoint. More information can be found in high-level prior art descriptions.
Wake-on-LAN (Local Area Network) is an Ethernet technology that allow nodes to be activated from a sleep mode by so called magic packets. If the node is turned off, or in a sleep mode, only the Network Interface Card (NIC) is listening on the Ethernet port, in low-power mode, hence the power consumption is reduced.
The magic packet is broadcasted on layer 2 of the Open Systems Interconnection (OSI) model and contains the Media Access Control (MAC) address of the node to be woken up. The NIC of a node in sleep mode that is part of the broadcast domain listens to the magic packet. The NIC triggers the powering up process if the MAC address equals the node MAC address string. That is the NIC signals the power supply or motherboard of the node to start the wakeup process.
The functionality is specified and implemented for both wired and wireless Ethernet networks.
Operators often want to measure the performance in their networks to assess quality of service, to do fault management or just measure trends to deliver high-quality services to their customers. One way to measure the end-to-end performance is to utilize active measurement protocols such as TWAMP at the IP layer or Y.1731 for Ethernet layer networks.
One approach in EPS is to deploy a TWAMP controller in the UE and initiate sending of ensembles of packets of TWAMP packets towards a centrally located TWAMP reflector. The reflector timestamps each packet and then return it to the source. This approach requires extensive management control of the UE and hence only a limited set of UEs can actually be used for performance monitoring. One of the management problems in this scenario is that the measurement data has to be stored in the UE and then later transported to an operator-controlled node. This further increases the load on the UE.
Another approach is to do the opposite by deploying simple reflectors in the UE. In this case the operator has full control of the active measurement sessions to be started and stopped, i.e. when to initiate sending of ensembles of packets of TWAMP sessions. Further, due to the design of TWAMP, if that specific protocol is used, all measurement data is readily available in the operator network during and after the measurement session.
One issue with active measurements is that the ensembles of packets that are sent through over the links and from, to and through elements in the paths of the network contributes to the activity level of the network. In particular, the periods of idle or sleep modes tend to be reduced. An opened or maintained radio bearer drains battery from the UE as well as increasing the signaling overhead in the E-UTRAN. This is in addition to the cost of injecting measurement traffic into the network.